Aspirating face seals are used to minimize leakage through a gap between two components, wherein such leakage is from a higher pressure area to a lower pressure area. Such seals have been used, or their use proposed, in rotating machinery. Such use includes, but is not limited to, turbomachinery including steam turbines and gas turbines used for power generation and gas turbines used for aircraft and marine propulsion. It is noted that aspirating face seals minimize the leakage of steam between a rotor and a stator in steam turbines and minimize the leakage of compressed air or combustion gases between a rotor and a stator in gas turbines.
A steam turbine has a steam path which typically includes, in serial-flow relationship, a steam inlet, a turbine, and a steam outlet. A gas turbine has a gas path which typically includes, in serial-flow relationship, an air intake (or inlet), a compressor, a combustor, a turbine, and a gas outlet (or exhaust nozzle). Gas or steam leakage, either out of the gas or steam path or into the gas or steam path, from an area of higher pressure to an area of lower pressure, is generally undesirable. For example, gas-path leakage in the low-pressure-turbine thrust-bearing area of a gas turbine, between axially opposing areas of a rotating cone of the rotor and an inner casing of the stator, will lower the efficiency of the gas turbine leading to increased fuel costs. Also, steam-path leakage in the turbine area of a steam turbine, between axially opposing portions of the rotor and stator, will lower the efficiency of the steam turbine leading to increased fuel costs.
Conventional aspirating face seals typically have the rotor configured as a first seal part, with the first seal part either being attached to, or being a monolithic portion of, the rotor. Likewise, such seals typically have the stator configured as a second seal part, with the second seal part either being attached to, or being a monolithic portion of, the stator. The first and second seal parts are generally annular, generally perpendicular to the longitudinal axis of the rotor, generally opposing, axially spaced apart, and proximate each other. Typically, the first part and the second part together define a radially extending air bearing and a radially extending air dam positioned radially inward of the air bearing. The air bearing surface of the first part and the air dam surface of the first part generally lie in the same plane. The air bearing surface of the second part has a hole which is an outlet for a first passageway connecting the hole with air from the higher pressure side of the seal. The stator has a second passageway which carries air, which has passed the air dam from the higher pressure side of the seal, to the lower pressure side of the seal. Known seal designs have also included an aspirator tooth extending from the stator axially across, and radially inward of, the air dam, with the aspirator tooth having a tip spaced apart from and proximate the rotor.
It is important to note that an aspirating face seal is a non-contacting seal in that the first and second parts of the seal do not touch. It is also important to note that aspirating face seal technology uses phrases such as "air bearing", "air dam", and "air flow", wherein it is understood that the word "air" is used to describe the working fluid of the seal. The working fluid of an aspirating face seal includes, without limitation, compressed air, combustion gases, and steam.
Applicants found that although mathematical modeling of an aspirating face seal predicted good seal performance with a small controlled leakage, a full scale test of such a seal, in an aircraft-engine gas-turbine configuration, yielded poor seal performance with a large controlled leakage. What is needed is an aspirating face seal capable of being used in a rotor and stator assembly, such as a rotor and stator assembly of a gas-turbine aircraft engine, with a small controlled leakage.